Apparatus for cleaning the heads of welding robots

ABSTRACT

Apparatus for cleaning the heads of electrical welding robots, the heads including a gas casing and an electrical contact nozzle. The apparatus includes an open vessel which has connected thereto one or more ultrasonic generators which function to generate ultrasonic waves in a liquid contained in the vessel. The vessel has mounted therein a rotary device which is located beneath the upper surface of the liquid. The rotary device operates as a mode stirrer to help loosen rings of weld material that have been deposited at the gas casing outlet. Additionally, wire brushes and cutting tools can be provided on the rotary device and rotationally driven to assist in weld material removal from the casing outlet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for cleaning the heads ofwelding robots.

2. Description of the Related Art

Welding robots are used generally within the workshop industry. Thisapplies primarily to MIG-welding and MAG-welding A welding robot isprogramed to follow a certain pattern of movements, i.e. the robot headis arranged to follow a given pattern of movements. A workpiece to bewelded by the robot is positioned accurately in relation to the robot,such that the workpiece will be located in a predetermined position inrelation to the robot. As the robot head moves through the predeterminedmovement pattern, it will move in a predetermined manner in relation tothe workpiece.

In welding operations, the robot head carries a welding head. The robotis thus able to move the welding head to those locations and along thoseedges or corresponding surfaces where welding is to be performed.

A welding head includes a gas casing which includes a central passagewayfor the delivery of welding gas. The gas is an inert gas and is ejectedonto the weld location to prevent oxidation of the melt and alsooxidation of those parts of the workpieces that are heated to hightemperatures in the welding process.

The gas casing passageway has a funnel-shaped orifice. An electricalcontact nozzle is provided in the gas-casing passageway and has acentral channel through which welding rod is advanced to the weldinglocation. The forward end of the nozzle terminates short of the orificeof the gas casing opening and is concentric therewith. The nozzle isconnected to one terminal of the welding unit voltage source and theworkpiece is connected to the other terminal of said source.

Splashes of weld material and slag, so-called weld spray, occur during awelding operation, these splashes landing on the weld head and therewithto a great extent on the edge surfaces defining the gas-casing opening,because the edge surfaces are located close to the workpieces during awelding operation. These splashes result in the build-up of rings ofmaterial around and in the opening on the weld head. The weld head andthe nozzle also include soot from the fumes generated in the weldingprocess.

The rings of weld-spray that build-up on the welding head and said edgesurfaces are electrically conductive and result in spark-over betweenthe rings and the workpieces, whereas the intention is for spark-over totake place between the weld electrode and the workpieces. This resultsin welding interruptions. The weldspray buildup may also preventsufficient gas from being delivered to the weld location through the gascasing, resulting in a poor quality weld.

The above-identified weld-spray ring is built-up to an unacceptable sizetypically in from five to tan minutes, meaning that the gas casing mustbe cleaned relatively often.

At present, the gas casing is cleaned by placing the gas-casing openingon a milling tool and milling away the weldspray ring mechanically. Thering is often seated very firmly on the gas casing and removal of thering results in the removal of material from the gas casing by virtue ofthe ring loosening from the casing and being whirled around in contactwith the casing by the milling tool, therewith causing wear to thecasing. The task of removing the ring with the aid of otherhand-operated tools, such as cutting nippers, for instance, is alsotime-consuming. The interior of the gas casing and the electricalcontact nozzle are cleaned with the aid of compressed air, although theresult is not always satisfactory.

The welding equipment may also include watercooled gas casings, whichare provided with internal cooling channels. Repeated cleaning of thegas casings with subsequent removal of material therefrom may result inthe removal of so such material as to open the cooling channels so thatthe water conducted therethrough will spray out. This results ininterruptions in the welding operation.

In view of the fact that gas casings are relatively expensive and thatthe casings must be cleaned very often, it is highly desirable for thecasings to be cleaned in a manner which is lass harsh on the casings andwhich will enable the casings to be cleaned much more quickly. It isalso desirable to be able to clean the inside of the gas casing and theelectrical contract nozzle quickly and simply.

The present invention satisfies these desiderata and provides anapparatus for cleaning the gas casing and the electrical contact nozzlequickly and with such less wear on the casing in the proximity of itsopening than that experienced with conventional cleaning processes.

SUMMARY OF THE INVENTION

The present invention thus relates to an apparatus for cleaning theheads of electrical welding robots, said heads including a gas casingand an electrical contact nozzle, wherein the apparatus includes an openvessel having connected thereto one or more ultrasonic generators whichfunction to generate ultrasonic waves in a liquid contained in thevessel; and in that a rotary device in mounted in the vessel with saiddevice located beneath the upper surface level of the liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, partly withreference to exemplifying embodiments of the invention and also withreference to the accompanying drawings, in which

FIG. 1 is a side view of part of an apparatus in accordance with thepresent invention;

FIG. 2 illustrates the apparatus of FIG. 1 from above;

FIG. 3 illustrates schematically a gas casing and an associatedelectrical contact nozzle, said casing being shown in section;

FIG. 4 in a side view of the apparatus of FIG. 1 and shown a vesselbelonging to said apparatus in section, taken on the line A--A in FIG.2;

FIGS. 5a, 5b and 5c illustrate different tools; and

FIG. 6 illustrates a rotary device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1, 2 and 4 illustrate an apparatus for cleaning the heads ofelectrical welding robots, said heads including a gas casing and anelectrical contact nozzle.

In accordance with the invention, the apparatus includes an open vessel1 which has connected thereto one or more ultrasonic generators 2, 3 forgenerating ultrasonic waves in a liquid 4 present in the vessel 1. Theultrasonic generators are of a conventional kind and of the type used togenerate ultrasonic waves it a liquid for cleaning purposes, in a knownmanner. The vessel 1 is preferably made of stainless steel. According tothe invention, there is mounted in the vessel a rotary device which islocated beneath the upper surface level of the liquid. This surfacelevel is shown by the undulating line 5 in FIG. 4.

The rotary device functions to stir the modes, i.e. standing waves aredisturbed in the liquid. This has been found to provide a markedlyimproved cleaning affect.

According to one preferred embodiment of the invention, the vessel 1 isconical in shape with the cone apex 6 facing downwards. The outer mantlesurface or the cone is provided with a plurality of flat sidepieces7-12. An ultrasound generator 2, 3 is mounted on each of three or moreof the flat sidepieces 7-12, to generate ultrasonic waves in the liquid.

According to one preferred embodiment, the vessel 1 includes sixsidepieces with an ultrasonic generator placed on each alternatesidepiece, i.e. an embodiment which includes a total or threegenerators.

The side surfaces define an angle v (see FIG. 4) with a plane whichextends perpendicular to the longitudinal axis 13 of the vessel and theultrasonic generators are so positioned on respective side surfaces thatrespective normals 14, 15 (see FIG. 1) of said side surfaces extendingfrom respective ultrasonic generators will coincide with a point 16 onthe longitudinal axis of the vessel 1 beneath the surface 5 of theliquid. As a result, strong interference taken place between theultrasonic waves at the point 16.

A shaft 17 extends through a penetrating hole 16' in the bottom of thevessel 1 and carries a tool attachment device 18 on the end thereoflocated in the vessel. An electric motor 48 which drives the shaft 17 iscoupled to the other end of the shaft.

According to one preferred embodiment, the shaft 17 is rotated at aspeed of 50 to 500 r.p.m., preferably about 180 r.p.m.

According to one preferred embodiment, the tool attachment device 18 hasthe form of a plate 19 which is positioned at right angles to the shaft17 and the upper side 20 of which is provided with tool-mounting means.

The tool attachment device 18 is preferably fitted detachably to theshaft 17. According to one embodiment, the upper part 21 of the shaft 17has a square cross-sectional shape, for instance. In this case, theattachment device 18 will include a sleeve 22 which projects down fromthe plate 19 and which has an internal hole of correspondingcross-section. When the sleeve 22 is fitted onto the upper part 21 ofthe shaft, the two parts will be in engagement for rotation of the tool.

The tool is comprised of one or more brushes and/or a milling tool.Examples of such tools are shown in FIGS. 5a-5c.

FIG. 5a shows a steel-wire brush 23 fitted on a base plate 24.

FIG. 5b shows a milling tool 25 having upstanding cutting edges 26. Theouter side of the cutting edges is intended to abut the inside of a ringof weld spray adjacent the opening of a gas casing. The milling tool ismounted on a base plate 27. The milling tool may have a form whichcorresponds to the form typically used to clean-off rings of weld spray.

FIG. 5c shows another cutting tool 28 having an upwardly rounded cuttingedge 29 which is intended to abut the ring of weld spray in the same wayas the milling tool. This cutting tool is mounted on a base plate 30.

The tool base plates 24, 27, 30 are fitted to the plate 20 of the toolattachment device in a manner which will prevent rotation of the baseplates on the plate 20. For instance, the plate 20 may be provided witha number of upstanding pegs 31-33 which are received in correspondingholes 34-36 in the base plates 24, 27, 30. Thus, when a tool in fittedto the attachment device 18, the tool will rotate as the shaft 17rotates.

FIG. 3 illustrates schematically a conventional gas casing 37 fitted toa robot head. The casing includes a sleeve 38 and an electrical contactnozzle 39. The nozzle 39 is screwed onto a pipe (not shown) and whenfitted takes the position shown in FIG. 3 relative to the sleeve 38. Asmentioned before, the nozzle 34 has provided therein a channel 40 inwhich welding rod 41 in advanced. As the welding rod 41 is consumed, therod is advanced down in the direction of the arrow 42. Inert gas flowndown between the sleeve 38 and the nozzle 39 when welding is in process,as indicated by the arrows 43.

As mentioned in the introduction, welding spray will build-up a ring ofmaterial around the edges defining the gas casing opening 44. The lowerpart of the casing 37 in the vicinity of the casing opening 44 in shownat the bottom of FIG. 3 in broken lines. A ring 45 of material of theaforesaid kind is shown in full lines in a normally occurring size.

Obviously, the presence of such a ring 45 of materials will disturb theflow of gas from the gas casing 37, furthermore, such a ring willinfluence the location at which an electric spark-over takes place onthe workpiece. It is, therefore, necessary to remove such rings.

The speed at which such a ring builds up will depend on how well thewelding parameters, such as voltage, current strength, welding speed,etc., have been set. It may take from a few minutes to an hour for sucha ring to build up. Each time a ring builds up, it in necessary toclean-off the ring in order not to impair the quality or the weld.

The present invention works in the following manner. When a gas casing37 is to be cleaned, the robot is programmed to move the casing to aposition corresponding to the position shown in broken lines, in FIG. 4,such that the forward part of the casing will be in contact with a tool24, 27, 30 mounted for rotation with the plate 19.

The level 5 or the liquid 4 in the vessel in sufficiently high to allowat least the forward part of the casing 37 and the electrical contactnozzle 39 to be submersed in the liquid.

According to one preferred embodiment, the liquid is a washingdetergent. The washing detergent may be any suitable detergent used forindustrial purposes. One example of a suitable washing detergent is thatsold by Leverindus, Nykoping, Sweden, under the trade designation ST104. The washing effect can be enhanced with the aid of vessel-mountedimmersion heaters (not shown), so as to maintain the liquid at anelevated temperature, for instance at a temperature of 60° C.

The ultrasonic generators are started up in conjunction with loweringthe gas casing 39 into the vessel 1 of the inventive device. It hassurprisingly been found that the ultrasonic waves cause the ring 45 toloosen from the casing 37 such that the ring will either fall off or canbe easily removed from the casing. The ring is seated initially veryfirmly to the casing, which is one of the main problems encountered whencleaning gas casings with the aid of conventional methods. At times, thering will simply fall from the casing when the casing is lowered downinto the inventive apparatus, without needing to use a tool to this end.In this regard, it has been found that the provision of a rotary devicein the vessel has a significant effect on the tendency of the ring toloosen, despite the rotary device not being in contact with the ring. Itis assumed that the mode stirring affect of a rotary device is highlyinfluential in this regard.

One such rotary device is shown by way of example in FIG. 6, in the formof a U-shaped device 46 mounted on a base plate 47. The base plate 47corresponds to the base plates 24, 27, 30. The device 46 is designed soas not to come into contact with the gas casing 37 when the casing islowered into the vessel 1. Such a rotary device can be referred to as amode stirrer.

It has been observed that the tendency of the ring 45 to loosen inparticularly manifest when the ring passes the region of the point 16(see FIG. 1), and consequently a construction which includes such apoint is highly essential.

A rotary milling tool is used to split rings which are relatively large,wherewith after having been loosened from the gas casing 37, the ring 45will split and fall therefrom. Naturally, the milling tool can also beused to cut away ring residues from around the gas-casing opening. Thecutting tool shown in FIG. 5c is used in a corresponding manner.

A brush can be used to clean the forward part of the casing 37 in agentler manner. The use of a brush will assume that the ring 45 has beenloosened from the casing by the ultrasonic vibrations, so that whenbrushed the ring will fall from the casing without requiring the use ofa milling or cutting tool.

It has been found that when applying the present invention, the ring 45of weld spray material is easily removed and that both the gas casingand the electrical contact nozzle 39 are cleaned very effectively.Furthermore, the time taken to clean the casing and the nozzle is onlyabout ten seconds. The problems mentioned in the introduction are,therefore, eliminated by means of the present invention. Because of theshort cleaning time afforded by the invention, the robot can beprogramed to perform gas casing cleaning operations at very shortintervals, so am to prevent the build-up of thick rings. This enableswelding to be performed with gas casings which are practically alwaysclean, therewith considerably improving the average weld quality.

Although the invention has been described with reference to a number ofexemplifying embodiments thereof, it will be understood that both theconstruction of the vessel and the number of ultrasonic generators usedand the design of the tools can be varied and modified by those skilledin this art.

The present invention shall not, therefore, be considered to be limitedto the aforedescribed embodiments, since variations and modificationscan be made within the scope of the following claims.

What is claimed is:
 1. Apparatus for cleaning the heads of electricalwelding robots, wherein the heads include a gas casing and an electricalcontact nozzle, said apparatus comprising: an open vessel having alongitudinal axis and which includes means for generating ultrasonicwaves in a liquid contained in the vessel, a rotary device within thevessel and located beneath an upper surface of the liquid, wherein thevessel is conical in shape and includes a cone apex that faces downwardsand is defined by a plurality of flat sidepieces, wherein the means forgenerating ultrasonic waves include an ultrasonic generator mounted oneach of at least three of the flat sidepieces for generating ultrasonicwaves in said liquid; and wherein normals extending inwardly from eachrespective ultrasonic generator coincide at a point on the longitudinalaxis of the vessel located beneath the upper surface of said liquid. 2.Apparatus according to claim 1, wherein the liquid level in the vesselis at an elevation such that at least a forward part of the gas casingand the electrical contact nozzle are immersed in the liquid. 3.Apparatus according to claim 1, wherein the vessel includes athrough-penetrating hole for receiving a shaft, wherein an end of theshaft positioned within the vessel carries a tool attachment device formounting tools for engaging the gas casing, and wherein an opposite endof the shaft is coupled to an electric motor for rotation of the shaft.4. Apparatus according to claim 3, wherein the shaft rotates at a speedof from about 50 to about 500 r.p.m.
 5. Apparatus according to claim 3,wherein the tool attachment device includes a plate which is positionedat right angles to the shaft, wherein an upper side of the plateincludes means for mounting a tool to the plate.
 6. Apparatus accordingto claim 5, wherein the tool includes a brush.
 7. Apparatus according toclaim 1, wherein the liquid is a washing solution containing adetergent.
 8. Apparatus according to claim 3, wherein the shaft rotatesat a speed of about 180 r.p.m.
 9. Apparatus according to claim 5,wherein the tool includes a milling tool.